1. Field of the Invention
The present invention relates to an inkjet recording apparatus, and more particularly, to an inkjet recording apparatus in which an air bubble in a flow channel in the vicinity of a pressure chamber which is not ejecting ink is expelled by being caused to vibrate resonantly to be borne away on a circulating flow of ink during printing.
2. Description of the Related Art
An inkjet recording apparatus (inkjet printer) has been known, which comprises an inkjet recording head (ink ejection head) having an arrangement of a plurality of nozzles and which forms images on a recording medium by ejecting liquid droplets of ink from the nozzles of the inkjet recording head toward the recording medium while causing the inkjet recording head and the recording medium to move relatively with respect to each other.
Various methods have been known as ink ejection methods for an inkjet recording apparatus. For example, a piezoelectric method is known, in which a diaphragm which constitutes a portion of each pressure chamber is deformed by the deformation of piezoelectric elements (piezoelectric actuators), thereby changing the volume of each pressure chamber, ink is introduced into each pressure chamber (ink chamber) via an ink supply passage when the volume of each pressure chamber is increased, and the ink in each pressure chamber is ejected from the nozzle in the form of an ink droplet when the volume of each pressure chamber is decreased.
In an inkjet recording apparatus having an inkjet recording head of this kind, ink is supplied to the inkjet recording head from the ink tank storing ink, via an ink supply channel (ink flow channel), and the ink can be ejected by means of various ejection methods. The nozzles of the inkjet recording head are filled with ink at all times in such a manner that printing can be carried out immediately whenever there is a print instruction.
However, if the ink in the head includes air bubbles, ejection defects may occur since the pressure generated in the pressure chambers is absorbed by the air bubbles rather than being transmitted correctly to the ink, and if the ink flow channels become blocked by air bubbles, dirt, or the like, then in the worst case, ejection failures may occur. In cases of this kind, conventionally, the ink is ejected (purged) forcibly by driving the piezoelectric elements, or the like, or the recording head is sealed hermetically with the cap and the ink including air bubbles, dirt, or the like, is suctioned out with a pump. However, during these operations, image recording must be interrupted.
Therefore, it is necessary to eliminate the air bubbles in the ink in the head, as far as possible. Consequently, in the related art, various methods for eliminating air bubbles in the ink have been proposed.
For example, Japanese Patent Application Publication No. 61-227061 discloses an inkjet recording apparatus in which, when the inkjet recording apparatus is not performing a recording operation, a vibration is applied to the ink in the ink flow channels including the nozzles of the recording head of the recording apparatus, in order to remove air bubbles, foreign material, or the like, in the ink flow channels, the energy of the aforementioned vibration being decreased gradually. Furthermore, according to Japanese Patent Application Publication No. 61-227061, the resonance frequency, for instance, of the substrate which constitutes the recording head is desirably used for the signal for excitation, and hence a frequency of 6 kHz to 13 kHz is desirably used for the signal for excitation, for example. Moreover, Japanese Patent Application Publication No. 61-227061 states that the frequency is swept repeatedly through a uniform frequency range.
Furthermore, Japanese Patent Application Publication No. 55-71567, for example, discloses an inkjet recording apparatus in which a vibrating body is provided in an ink supply port, a vibration is applied by the vibrating body to ink which is caused to flow by means of a pressure applied to an ink tank, and air bubbles attached to the inner walls of an external chamber float into the ink due to this vibration and are expelled via air bubble expulsion ports and removed.
Moreover, for example, Japanese Patent Application Publication No. 63-295267 discloses a restoration method for an inkjet recording apparatus in which a head is capped and ink in the liquid channels of the head is suctioned by a pump, while simultaneously the ink is made to vibrate by driving the head by applying a signal to the head driver, thereby making it easier to remove air bubbles which are attached to the inner walls of the liquid channels. During this operation, since the resonance frequencies of the air bubbles in the liquid channels vary according to the size of the air bubbles, then the frequency at which the head is driven is changed (swept).
Furthermore, Japanese Patent Application Publication No. 63-94848, for example, discloses a head protection apparatus for an inkjet printer in which the nozzle section of a head is covered with a cap, and while suctioning ink by means of a pump, air bubbles adhering to the walls of the spray channel system are made to float into the ink by firstly driving the piezoelectric elements of the head at a high frequency, and then gradually lowering (sweeping) the drive frequency to a low frequency range, in other words, a frequency band in which air bubbles floating in the ink collide with the walls of the spray channel system without adhering to the walls, and where cavitation does not occur.
However, in the related art, as described in the various patent references cited above, for example, the composition almost always involves removing air bubbles by capping the nozzles and suctioning with a pump while applying a vibration to the ink in order to detach air bubbles from the walls of the flow channels. In a composition of this kind, it is not possible to use the air bubble removal function during execution of a printing operation, and therefore printing operations have to be interrupted when air bubbles are to be removed.
Consequently, if continuous printing is being carried out by means of a single-pass printer which uses a page-wide full line head, then if the related art technology described above is used, operations for interrupting printing, capping the nozzles and suctioning with a pump are required in order to remove air bubbles, and therefore the productivity declines markedly.